It is desirable in some fields to apply pressure sensitive adhesive to a paper substrate and several methods are known for performing this process. German patent application 36 06 199, for example, discloses a method and apparatus for applying pressure sensitive adhesive on a continous web of paper. The web is coated with a primer, or adhesion promoter and dried in a first drying station. Next, an optional low adhesion backsize, or release layer, may be coated onto the opposite surface of the web and dried at a second drying station. Finally, a circulating intermediate carrier applies the pressure sensitive adhesive, which has been partially dried while on the intermediate carrier, over the primer layer. The paper web may then be collected and further processed as desired.
The various drying steps disclosed in the '199 patent (drying the primer layer, drying the low adhesion backsize layer, and drying the adhesive layer while on the intermediate carrier) remove moisture from the aqueous primer, backsize and adhesive materials, to prevent the paper web from curling or wrinking. However, the sequential application and drying of the primer and low adhesion backsize layers typically result in some curling of the paper web, which is undesirable. The curling problem would be more pronounced in the context of the application of a primer, low adhesion backsize, and adhesive to individual paper sheets rather than a paper web, because the web is typically in tension whereas the individual sheets are not. Thus, the method and apparatus of the '199 patent typically is not suitable for use with individual paper sheets.
It is therefore desirable to provide a method and apparatus for applying primer, low adhesion backsize, and pressure sensitive adhesive to a plurality of individual paper sheets without inducing curling or cockling of the sheets.